1. Field of the Invention
The present invention relates to a vehicle theft detection system.
2. Description of Related Art
In a previously proposed vehicle theft detection system, when an abnormal tilt of a vehicle is sensed by a tilt sensor in a parked state of the vehicle, vehicle position information, which is sensed through a global positioning system (GPS), is transmitted along with an abnormality signal from the vehicle theft detection system to a predetermined destination. For example, the abnormal tilt of the vehicle may be sensed by the tilt sensor to sense stealing of the vehicle when front wheels of the vehicle are lifted and towed by a wrecker without a notification to a user of the vehicle. A previously proposed vehicle theft prevention system generates a warning based on the detection of the stealing of the vehicle, which is detected by the vehicle theft detection system to limit or prevent stealing of the vehicle.
For example, Japanese Unexamined Patent Publication No. H09-240432 teaches a technique, which uses a tilt sensor. According to this technique, when the front wheels of the vehicle are lifted by, for example, a wrecker to tow the vehicle without a notification to a user or an owner of the vehicle, a tilt of the parked vehicle significantly changes, and this tilt of the vehicle is sensed by the tilt sensor to detect the stealing of the vehicle.
In the above vehicle theft detection system, which detects the abnormal tilt of the vehicle thorough the tilt sensor, when the vehicle is parked on a pallet of a pallet type multilevel parking facility, a normal tilt of the vehicle caused by the vertical movement of the pallet may be erroneously sensed as the abnormal tilt although the vehicle is kept parked safely. Furthermore, in a case where the vehicle is transported by a ferry along the sea, when the ferry is tilted by swing movement of the ferry caused by wave motion of the sea, this normal tilt of the vehicle may be erroneously sensed as the abnormal tilt. That is, the prior art vehicle theft detection system cannot distinguish a change in the tilt of the vehicle caused by the stealing of the vehicle from the normal tilt of the vehicle, which is caused by the incident other than the stealing of the vehicle, thereby resulting in an erroneous detection of the stealing of the vehicle.
In view of the above disadvantage, Japanese Unexamined Patent Publication No. 2003-34233 discloses an improved vehicle theft detection system that allows a user of a vehicle to change an operational mode of the vehicle theft detection system from one to another. These operational modes include a parking mode, a multilevel parking mode and a release mode. The parking mode is set when the user leaves the vehicle. The multilevel parking mode is set when the vehicle is parked in the multilevel parking facility. The release mode is set when the user uses the vehicle. When the vehicle is parked in the multilevel parking facility, the user sets the multilevel parking mode. In the multilevel parking mode, even when the tilt sensor senses an abnormal tilt of the vehicle in the parked state of the vehicle, the vehicle theft detection system will not determine that the vehicle is stolen. In this way, the erroneous detection of the stealing of the vehicle can be avoided.
However, in the case of the vehicle theft detection system of Japanese Unexamined Patent Publication No. 2003-34233, the user may forget to set the multilevel parking mode at the time of parking the vehicle in the multilevel parking facility and may leave the vehicle while setting the vehicle theft detection system in the parking mode. In such an instance, the tilt sensor senses the tilt of the vehicle, which is caused by the movement of the pallet, as the abnormal tilt, and thereby the vehicle theft detection system may erroneously determine that the vehicle is stolen.